1) Field of the Invention
The present invention relates to a machining tool for manufacturing radial bearings, which is used to finish the inner circumference surface of a bearing hole in a radial bearing, and a manufacturing apparatus and a manufacturing method using the same. In particular, the present invention is suitable for use on dynamic pressure bearing devices that require high precision.
2) Related Art
Rotation drive devices generally use various types of radial bearing, such as, for example, metal bearings, sintered bearings and dynamic pressure bearings. In the manufacture of such radial bearings, the inner surface of a bearing hole is machined, which is usually done by cutting (lathe machining). For example, first, the diameter of a guide hole is enlarged through a rough machining, and in the subsequent finishing the inner circumference surface of the bearing hole is finished to a predetermined precision with a designed inner diameter dimension, surface roughness and roundness.
However, in the process of finishing the inner surface of a bearing through cutting (lathe machining), sawed marks and wavy marks remain as a result of the machining work. This makes it possible only to finish the inner surface of the bearing at most at a precision level with an inner diameter tolerance of xc2x12 xcexcm, a surface roughness of about 0.2RA, and a roundness of about 0.5 xcexcm. When trying to achieve a higher precision finishing in particular with a dynamic pressure bearing device, the processing time increases dramatically and an expensive comb tooth-shaped high precision automatic lathe must be used, which considerably reduce productivity. In addition, due to such problems in machining, there are substantial limitations in the bearing characteristics of the various bearing members mentioned above, and it is extremely difficult to obtain high-performance bearing members at low costs.
It is an object of the present invention to provide a machining tool for manufacturing radial bearings that can finish the inner circumference surface of a high precision bearing at low costs, and a manufacturing device and a manufacturing method using the same.
In accordance with one embodiment of the present invention, a machining tool for manufacturing a radial bearing, and a manufacturing apparatus and a manufacturing method using the machining tool may include an inner surface finishing tool to finish an inner circumference surface of a bearing hole provided on a radial bearing. The inner surface finishing tool may include a tool shaft main body member whose length generally corresponds to the length of the bearing hole in the axial direction. The tool shaft main body member has a hollow storage section. A rotatable core piece member with a circular cross-section is provided inside the hollow storage section in a manner moveable within the tool shaft main body member. A plurality of roll machining members each having a circular roll machining surface are provided about the rotatable core piece member. The plurality of roll machining members rollably abut against the outer circumference surface of the rotatable core piece member. The plurality of roll machining members are brought in contact under pressure with the inner circumference surface of the bearing hole. In one aspect of the present invention, the rotatable core piece member is movable in the radial direction and can be tilted with respect to the central axis of the tool shaft main body member.
As a result, when the finishing tool with roll machining members is inserted into the bearing hole even as the central axes of the finishing tool and the bearing hole are displaced in parallel or have a tilt angle with respect to each other, the plurality of roll machining members would come in contact with the inner circumference surface of the bearing hole as they rotate at a uniform velocity around the rotation core piece member. As a consequence, a uniform pressure is applied to the inner circumference surface of the bearing hole to cause an automatic center-aligning action to take place. Due to the automatic center-aligning action, the rotatable core piece member is forced to move in the radial direction and/or tilt against the central axis of the tool shaft main body member, thereby aligning with the central axis of the tool shaft main body member. As a result, the central axis of the machining diameter that connects the outer most circumference surfaces of the plurality of roll machining members aligns automatically and in high precision with the central axis of the bearing hole; and the machining by the roll machining members begins in a state in which the axes of these members are aligned with high precision. Thereafter, due to the pressing action of the roll machining members, the inner circumference surface of the bearing can be finished in high precision without sawed marks or wavy marks as one would see in cutting.
In accordance with one embodiment of the present invention, a gap xcex4 may be formed in the radial direction between the outer circumference of the rotatable core piece member and the inner circumference surface of the hollow storage section of the tool shaft main body member that would allow free movement of the rotatable core piece member, such that the movement of the rotatable core piece member in the radial direction and/or in the shaft tilt direction can be made easily and reliably using the gap in the radial direction.
Furthermore, in accordance with one embodiment of the present invention, the roll machining surface of each of the roll machining members may have a length L in the axial direction that is the same or longer than a machining diameter D that is defined by a circle connecting the outer most circumference surfaces of roll machining surfaces of the roll machining members. As a result, the roll machining members would abut against the inner circumference surface of the bearing hole in the range of the length L in the axial direction and be able to move in the radial direction or tilt in the axial direction within this abutting range. This causes the uniform velocity rotation of the roll machining members to be conveyed well to the inner circumference surface of the bearing hole and ensures the automatic center-aligning action to take place.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the invention.